High Temperature Nanocharacterization of Al/SiC Laminated Composite

Abstract

Metal-ceramic laminated composites exhibit attractive mechanical properties including high strength, high toughness, and damage tolerance. However, there is very little information available about their behavior at elevated temperatures due to the limitations of macro scale high temperature characterization techniques. In this study, the hardness and elastic modulus of aluminum/silicon carbide (Al/SiC) nanolaminates have been investigated within the temperature range of 23 to 450ºC using isothermal hot stage nanoindentation. Alternating layers of aluminum and silicon carbide -each with an average thickness of 20 and 22nm, respectively- were deposited on a silicon wafer, Si (111) substrate using a combination of DC and RF magnetron sputtering techniques. The hot stage nanoindentation tests were carried out using thermally stable cubic boron nitride Berkovich nanoindenter. Both the sample and the indenter were heated separately during the experiments to temperatures of 150, 300, and 450ºC while the nanoindentation chamber was purged with argon gas to retain oxygen level below 1.5% to deter oxidation of the sample. The cross section of the sample was also examined by scanning electron microscopy (SEM). The experimental results revealed that the hardness decreased with increase of temperature up to 300ºC. However, the elastic modulus increased up to at 150ºC after then it consistently declined with elevating the temperature. Interestingly, slight increase of the hardness was observed at 450ºC. Moreover, the plastic deformation of the sample at this temperature was smaller than that observed at 300ºC. This behavior is likely due to microstructural changes of the Al/SiC nano-films following a chemical reaction between thin layers at temperatures beyond 300ºC.